1. Field of the Invention
The present invention relates to blood sampling systems and, in particular, to an improved blood sampling device usable in such systems, and enabling in-line sampling.
2. State-of-the-Art
Arterial and venous infusion lines are used to introduce fluids into the blood stream of a patient. Devices of various types have long been used to regulate the flow of fluid from a fluid supply to an injection site. Typically the injection site is also used to take periodic blood samples from the patient.
In such an instance, the flow of fluid from the fluid supply can be turned off to allow blood to flow in the reverse direction through the arterial line to facilitate taking such blood samples. Patient requirements and the treatment protocol prescribed will dictate the frequency of the blood sampling procedure. When the frequency of sampling becomes greater, according to the needs of the patient and the treatment protocol, it becomes desirable to improve the efficiency of the blood draw procedure and eliminate waste whenever possible.
A particular situation of note relates to neonatal patients in which the blood supply is considerably smaller than the blood supply of adults and the need to maximize efficiency in the blood sampling procedure and to avoid unnecessary discharge of blood is of particular concern.
A known sampling procedure for drawing blood from an arterial line utilizes a plurality of stopcock mechanisms that prevent the flow of fluid from the fluid source and allow blood to flow from the patient into a collecting syringe connected to a removal port formed in one of the stopcocks. However, such a procedure necessarily will draw a mixture of fluid and blood in the first iteration of the sampling procedure, and the initial sample is discarded. A second sample is then taken, such second sample considered to be a representative sample of blood. Because the discarded sample includes not only fluid from the fluid source, but some of the patient's blood, such a two-sample process causes an unnecessary loss of blood to the patient. Other undesirable effects associated with the above noted sampling process includes the increased potential for introduction of air into the arterial line and the increased potential for introduction of contaminants into the patient's bloodstream.
An effort to modify the above noted two-step sampling process is noted in U.S. Pat. No. 4,673,386 entitled "Blood Sampler Device" and issued to Gordon. Gordon describes a mechanism for eliminating the need to undertake a two-step process to withdraw blood through an arterial line. The Gordon device comprises a combination pump/storage mechanism which accommodates the return flow of the downstream fluid such that a single sample can be taken from a removal port, that sample being clear of supply fluid and therefore representative of the patient's blood supply. The Gordon patent describes a method and apparatus for drawing blood from an injection site through an arterial line connected to a fluid supply.
The apparatus includes a variable capacity pump mechanism also having an interior chamber, first and second ports connected to the variable capacity interior chamber, and a retractable piston disposed within the housing to traverse within the chamber. A piston sealing member is provided about the chamber in slidable sealing relationship with the chamber to cause fluid to be drawn into the chamber, thereby facilitating extraction of the blood sample along the arterial line without the need to discharge an initial sample containing disproportionate amounts of supply fluid.
However, the Gordon device incorporates features which may be undesirable to a caregiver conducting the sampling process. For example, although the Gordon device is in fluid communication with the arterial lines transmitting fluid to the patient, the variable capacity chamber is disposed transverse to such line to cause an imbalance in such arterial line both prior to and during the sampling process. Moreover, the above-noted imbalance in the dual variable capacity storage device of Gordon is exacerbated during the sampling process making it difficult for a single attendant to conduct the sampling process. Although Gordon introduces certain desirable features to the sampling process, its awkward structure, and its bulkiness may be undesirable to the sampling process.